1. Field of the Invention
The present invention relates to a pickup level control device for a system for reading out recorded information, and more specifically to a device for controlling the level of an output signal from photoelectric converting elements of a pickup for an optical system for reading out recorded information.
2. Description of Background Information
In an optical system for reading out recorded information, for example, a read out laser beam is applied, via an object lens, as a light spot on a recording surface of a recording medium. With this arrangement, a signal corresponding to the recorded information is reproduced from an output signal of a photo detector for the photoelectric conversion, which detects a reflectd light of the incident laser beam from the recording surface of the recording medium. However, due to a deviation of the reflection factor, for example, according to the shape of pits on the recording disc used as a recording medium and/or due to a deviation of the sensitivity of the photo dectector, the level of a pickup signal, i.e., an output signal of the photoelectric transducer tends to vary widely. Accordingly, if the output signal level of the photoelectric transducer is exceedingly high, there is a risk that a circuit for processing the signal at a further stage will be saturated, which will result in a number of faults in the reproduced information. Such a variation of the output level of the photoelectric transducer is disadvantageous especially when a recording disc on which a Pulse Code Modulation (PCM) signal is recorded as recorded information. The reproduction of the recorded information is executed by amplifying the output signal of the photoelectric transducer and then campared with the amplified signal with a predetermined reference level. More specifically, an asymmetrical ac (alternating current) signal, that is, an ac signal with clipped positive peaks for example, will be obtained if the amplifying stage is saturated. As mentioned above, this is quite disadvantageous in the case of the PCM process since normally a zero level comparator is used as the level comparator. In short, there is a risk in the conventional arrangement that false data of a recording signal will be obtained by a zero level comparison of such an asymmetrical ac output signal.